Hanson 10e Pp Ts Ch04

Homeostatic Systems and Drugs

Chapter 4

Homeostasis

Internal and external changes in the environment

Body self-regulates viaNervous system & Endocrine system

Equilibrium

Introduction to Nervous Systems

• All nervous systems consist of specialized nerve cells called neurons.

• Neurons are responsible for conducting the homeostatic functions of the brain and other parts of the nervous system by receiving and sending information.

• Sending and receiving information is an electrochemical process.

Transfer of Messages by Neurons

• The receiving region of the neuron is affected by a chemical message that either excites or inhibits it.

• Excitatory message- impulse moves from the receiving region of the

neuron down the axon to the sending region (terminal)

- chemical messengers (neurotransmitters) are released

Transfer of Messages by Neurons (continued)

• Neurotransmitters travel and attach to receiving proteins called receptors on target cells.

• Activation of receptors causes a change in the activity of the target cell; the target cells can be other neurons or cells that make up organs, muscles, or glands.

Sending Messages by Neurons

Neurons and Neurotransmitters

• Neurons can send discrete excitatory or inhibitory messages to their target cells.

• Neurons are distinguished by the type of neurotransmitter they release.

• Neurotransmitters represent a wide variety of chemical substances and functions.- Example: Dopamine activates the pleasure

center.

Common Neurotransmitters

Neurotrans-mitter

Type of Effect

CNS Changes

Drugs of Abuse

Dopamine inhibitory-

excitatory

euphoria

agitation

paranoia

altered

amphetamines,

Cocaine

GABA inhibitory cognition

sedation

relaxation

drowsiness

depression

alcohol,

Valium-type

barbiturates

Common Neurotransmitters (continued)

Serotonin inhibitory sleep

relaxation

sedation

LSD

Acetylcholine excitatory-

inhibitory

mild euphoria

excitation

insomnia

tobacco,

nicotine

Endorphins inhibitory mild euphoria

block pain

narcotics

Neurons

• Dendrites—the receiving regions of a neuron’s cell body.

• Each neuron in the central nervous system is in close proximity with other neurons.

• Although they are close, neurons never actually touch.

Neurons (continued)

• Synapse—the point of communication between one neuron and another

• Synaptic cleft—the gap between neurons at the synapse

Neurons

Synapses

• Excitatory synapse—initiates an impulse in the receiving neuron when stimulated, causing release of neurotransmitters or increasing activity in target cell

• Inhibitory synapse—diminishes likelihood of an impulse in the receiving neuron or reduces the activity in other target cells

Synapses (continued)

• A receiving neuron or target cell may have many synapses.

• Final cellular activity is a summation of these many excitatory and inhibitory synaptic signals.

Drug Receptors

• The chemical messengers from glands and neurons exert their effects by interacting with special protein regions in membranes called receptors.

• Receptors only interact with molecules that have specific configurations.

Drug Receptors(continued)

Drug Receptors (continued)

• Agonists—substances or drugs that activate receptors

• Antagonists—substances or drugs that attach to receptors and prevent them from being activated

Drug Receptors(continued)

Neurotransmitters

• Many drugs affect the activity of neurotransmitters by altering their synthesis, storage, release, or deactivation.

• Neurotransmitters frequently altered by drugs of abuse:- Acetylcholine- Catecholamines- Serotonin- GABA- Endorphins

Major Divisions of the Nervous System

• Two major components of the nervous system

- Central nervous system (CNS)

- Peripheral nervous system (PNS)

Central Nervous System

• CNS

- Brain

- Spinal cord

• CNS receives information from PNS, evaluates information, then regulates muscle and organ activity via PNS

Central Nervous System

• Reticular activating system- Receives input from all the sensory systems and

cerebral cortex- Controls the brain’s state of arousal (sleep vs.

awake)• Basal ganglia

- Controls motor activity• Limbic system

- Regulates emotional activities, memory, and endocrine activity

- Dopamine

Central Nervous System (continued)

• The cerebral cortex- Helps interpret, process, and respond to

information

• The hypothalamus- Controls endocrine and basic body functions

Central Nervous System Structure

Peripheral Nervous System

• Consists of input and output nerves

• Input to brain and spinal cord- Conveys sensory info (pain, pressure,

temperature)

• Output—two types- Somatic (control of voluntary muscles)- Autonomic (control of unconscious functions)

Autonomic Nervous System

• Sympathetic and parasympathetic system- These systems work in an antagonistic fashion

to control unconscious, visceral functions such as breathing and cardiovascular activity

• Sympathetic system- Norepinephrine

• Parasympathetic system- Acetylcholine

Autonomic Nervous System Structure

Introduction to the Endocrine System

• The endocrine system consists of secreting glands (e.g., adrenal, thyroid, pituitary)

• These glands produce substances called hormones (e.g., adrenaline, steroids, insulin, and sex hormones)

• These substances are information transferring molecules

Introduction to the Endocrine System (continued)

• Hormones are secreted into the bloodstream and carried by the blood to all the organs and tissues of the body.

• Hormones affect selected tissues that are designed to receive the information.

• Hormones may be highly selective or very general with regard to the cells or organs they influence.

Introduction to the Endocrine System (continued)

The Abuse of Hormones:Anabolic Steroids

• Androgens- Produce growth of muscle mass- Increase body weight

• Anabolic steroids - Are structurally related to the male hormone

testosterone- Sometimes abused by athletes and body

builders to improve strength and appearances